1. Field of the Invention
The present invention relates generally to microwave antennas and, more specifically, to a miniaturized directional microwave antenna for microwave therapy purposes that is highly suitable for use in catheters or syringes where limited space is available.
2. Description of Prior Art
Microwaves are utilized in various medical treatments. As one possible example, microwave ablation therapy may be utilized to treat damaged heart tissues or other tissues containing malignant or harmful cells. During microwave ablation treatments, the damaged tissue to be ablated may be located in one azimuthal direction with respect to the antenna whereas healthy tissue may be positioned in another azimuthal direction with respect to the antenna. It may often be desirable to ablate the damaged tissue by producing therein an increase in temperature while simultaneously limiting the increase in temperature in the healthy tissue.
Antenna directionality implies a focusing of energy. Higher antenna directionality or focusing generally requires a larger size antenna due to the need to provide antenna focusing elements or means. Non-limiting examples of focusing elements may comprise parasitic and/or active antenna elements, reflectors, directors, and the like. Within the small confines of a small diameter catheter or a syringe, there is seldom sufficient room for an aperture large enough to provide antenna directionality.
Several variations of monopole antennas have been used in the prior art for supplying RF or microwave frequency electromagnetic radiation in medical applications, often through the use of a catheter. These antennas typically have the property that radiation around the antenna (azimuthal radiation) is fairly symmetric. This can be disadvantageous in many instances, as discussed above, in which directionality is preferred in order to protect tissue on one side of the antenna while supplying energy to the opposite side.
In some prior art applications, a catheter-based antenna has been routed to an organ wherein sufficient interior space is available that permits expansion of the antenna. The antenna expands in order to increase the aperture size of the antenna, and hence, the directivity, e.g., Gu, Z., Rappaport, M., Wang, P. J., and VanderBrink, B. A., “Development and experimental verification of the wide-aperture catheter-based microwave cardiac ablation antenna”, IEEE Trans. On Microwave Theory and Techniques, vol. 48, November 2000). Accordingly, these antennas are limited to use in special regions of the body.
The following patents disclose prior art efforts related to the above-described and/or other problems and studies:
U.S. Pat. No. 4,204,549, issued May 27, 1980, to Paglione discloses an apparatus for hyperthermia treatment that provides transmission of microwave energy for irradiation of tissues and simultaneous and concurrent and continuous measurement of the temperature of the heated tissues at the site of the treatment. The microwave energy is supplied to the site of treated tissue by a coaxial applicator, which is positioned near the tissue.
U.S. Pat. No. 4,311,154, issued Jan. 19, 1982, to Sterzer et al discloses an apparatus that uses microwave energy for the therapeutic and hyperthermic treatment of an internal body organ such as the prostate gland. An irregularly shaped coaxial applicator having a narrow portion and a wide portion is inserted through the male anus into the rectum such that a substantially maximum intensity of the microwave energy irradiates the prostrate gland for preferential heating of the prostate gland and a substantially minimum intensity irradiates untreated tissue. Temperature sensing means are positioned on the periphery of the applicator to measure the tissue environment irradiated by the microwave energy. A controller, operating with the temperature sensing means, is provided to maintain the temperature of the tissue environment within a desired temperature range.
U.S. Pat. No. 4,601,296, issued Jul. 22, 1986, to Yerushalmi, discloses an apparatus for hyperthermic treatment of tumors comprising a probe insertable into a body cavity in the vicinity of a tumor to be treated, the probe including a radiation emitting antenna and a conduit system for the passage of a cooling fluid adjacent the outer surface thereof for cooling of tissue lying adjacent the probe.
U.S. Pat. No. 4,776,086, issued Oct. 11, 1988, to Kasevich et al., discloses a microwave collinear antenna array applicator for in situ or in vivo treatment of tumors and/or other materials by hyperthermia. The array consists of a plurality of harmonically related resonant coaxial antenna elements connected electrically in series to provide uniform heating along the entire length of the array. At the distal end of the array, a resistor may be provided at the inner conductor for steering the heating pattern. At the proximal end of the array, an impedance matching dielectric structure is provided to enable maximum power transfer to the array and to minimize stray leakage currents along the outside of the coaxial transmission line. The array may be made longer or shorter without changing frequency and therefore, depth of penetration by simply adding or subtracting half-wave resonant elements or sections of coaxial transmission line. A lossy sleeve member may be provided around the applicator to provide a localized source of heat.
U.S. Pat. No. 5,026,959, issued Jun. 25, 1991, to Ito et al., discloses an invention that relates to a microwave radiator for warming therapy inserted into a human body to cure focuses of the body such as tumors. It has a first and second high-frequency coaxial cable. The second high-frequency coaxial cable has an inner conductor and a plurality of ring conductors disposed at the outer periphery of the inner conductor via a dielectric. The second high-frequency coaxial cable is inserted into the focuses of the body, and warming therapy can be conducted using radiated electromagnetic waves.
U.S. Pat. No. 5,151,100, issued Sep. 29, 1992, to Abele et al., discloses a catheter device and method for heating tissue. The device has a catheter shaft constructed for insertion into a patient's body, and at least one chamber mounted on the catheter shaft. The catheter shaft has at least one lumen for fluid flow through the shaft. The chambers are defined by walls that are at least in part expandable. Fluid flows, through the lumens, between the chambers and a fluid source outside the body. The chambers can be filled with the fluid after they have been placed within the body. A heating device heats liquid within at least one of the chambers, so that heat is transmitted from the liquid to surrounding tissue by thermal conduction through the wall of the chamber. Means are provided for selectively directing heat transmission toward a selected portion of surrounding tissue. The chambers are fillable with fluid separately from each other, so that the chambers can occupy any of a plurality of possible total volumes. By selecting the total volume of chambers, compression of the tissue can be controlled, and hence the effectiveness of transfer of heat to the tissue can be controlled. According to the method, the catheter device is used to heat tissue from within a duct in a patient's body. The chambers are inserted into the duct and filled with fluid. Liquid is heated within at least one of the chambers, and heat is selectively directed toward a selected portion of surrounding tissue.
U.S. Pat. No. 5,314,466, issued May 24, 1994, to Stern et al., discloses an assembly for steering and orienting a functional element at the distal end of a catheter tube that holds the functional element with its major axis aligned with the axis of the catheter tube for convenient steering to a tissue site. The mechanism can also pivot the functional element in response to an external force to orient the major axis of the functional element generally parallel to the plane of the tissue site, without bending the catheter tube.
U.S. Pat. No. 5,323,778, issued Jun. 28, 1994, to Kandarpa et al., discloses a method for imaging and heating body tissues with one probe, through use of a magnetic resonance imaging radio frequency source. The device may also be configured with a thermocouple to provide temperature-controlled heat therapy with sufficient image definition to control that therapy.
U.S. Pat. No. 5,370,644, issued Dec. 6, 1994, to Langberg, discloses a cardiac ablation apparatus including a solenoidal antenna, monitoring electrodes, and a coupling network at a distal end of a catheter transmission line, and another coupling network at the proximal end of the catheter transmission line to connect the catheter to the source of radiofrequency (RF) power and to an intracardiac electrogram monitor. Solenoidal antenna design includes single and multiple windings with varying geometrical features. Plated plastic tri-axial design of a transmission line offers unitary fabrication. A catheter with variable impedance electrode and gap coatings has features useful for both ablation and for hyperthermia applications.
U.S. Pat. No. 5,694,134, issued Dec. 2, 1997, to Barnes, relates to a phased array antenna for microwave and millimeter wave applications, using either microstrip line, coplanar waveguide, or other construction techniques incorporating a solid dielectric transmission line. A continuously variable phase delay structure which is used to control the beam pattern of the phased array antenna can be applied to the construction of resonant frequency tunable coplanar waveguide antennas and impedance tunable quarter-wave transformers. A thin film of barium strontium titanate or other nonlinear material is deposited upon the coplanar waveguide, and/or the patch antenna element. The dielectric constant of the thin film can be made to vary significantly by applying a DC voltage to the thin film. The propagation constant of a transmission line is directly proportional to the square root of the effective dielectric constant (assuming a lossless dielectric). In an array of multiple antenna elements provided with the feed structure using the disclosed transmission lines, the direction of the resultant main beam of the array can be made to vary over a complete half-sphere with only two adjustable DC voltages applied to the dielectric thin films.
U.S. Pat. No. 5,843,144, issued Dec. 1, 1998, to Rudie et al., discloses a method for treating an individual with diseased prostatic tissue, such as benign prostatic hyperplasia, includes inserting a catheter into a urethra to position a microwave antenna located within the catheter adjacent a prostatic region of the urethra. A microwave antenna is then driven within a power range for applying microwave energy substantially continuously to prostatic tissue to heat the prostatic tissue surrounding the microwave antenna at a temperature and for a time period sufficient to cause necrosis of the prostatic tissue.
U.S. Pat. No. 5,904,709, issued May 18, 1999, and other patents, to Arndt et al., disclose an exemplary method and apparatus for propagating microwave energy into heart tissues to produce a desired temperature profile therein at tissue depths sufficient for thermally ablating arrhythmogenic cardiac tissue to treat ventricular tachycardia and other arrhythmias while preventing excessive heating of surrounding tissues, organs, and blood. A wide bandwidth double-disk antenna is effective for this purpose over a bandwidth of about six gigahertz. A computer simulation provides initial screening capabilities for an antenna such as operating frequency, power level, and power application duration. The simulation also allows optimization of techniques for specific patients or conditions. In operation, microwave energy between about 1 gigahertz and about 12 gigahertz is applied to monopole microwave radiator having a surface wave limiter. A test setup provides physical testing of microwave radiators to determine the temperature profile created in actual heart tissue or ersatz heart tissue. Saline solution pumped over the heart tissue with a peristaltic pump simulates blood flow. Optical temperature sensors disposed at various tissue depths within the heart tissue detect the temperature profile without creating any electromagnetic interference. The method may be used to produce a desired temperature profile in other body tissues reachable by catheter such as tumors and the like.
U.S. Pat. No. 6,245,062, issued Jun. 12, 2001, to Berube et al., discloses a directional reflective shield assembly for a microwave ablation instrument having an antenna coupled to a transmission line. The antenna is formed to generate an electric field sufficiently strong to cause tissue ablation. The shield assembly includes a cradle device disposed about the antenna in a manner substantially shielding a surrounding area of the antenna from the electric field radially generated therefrom. The cradle device further provides a window portion communicating with the antenna which is strategically located relative the antenna to direct a majority of the field generally in a predetermined direction.
U.S. Pat. No. 6,289,249, issued Sep. 11, 2001, and other patents, to Arndt et al., disclose an exemplary method, simulation, and apparatus that are highly suitable for treatment of benign prostatic hyperplasia (BPH). A catheter is disclosed that includes a small diameter disk loaded monopole antenna surrounded by fusion material having a high heat of fusion and a melting point preferably at or near body temperature. Microwaves from the antenna heat prostatic tissue to promote necrosing of the prostatic tissue that relieves the pressure of the prostatic tissue against the urethra as the body reabsorbs the necrosed or dead tissue. The fusion material keeps the urethra cool by means of the heat of fusion of the fusion material. This prevents damage to the urethra while the prostatic tissue is necrosed. A computer simulation is provided that can be used to predict the resulting temperature profile produced in the prostatic tissue. By changing the various control features of the catheter and method of applying microwave energy a temperature profile can be predicted and produced that is similar to the temperature profile desired for the particular patient.
U.S. Pat. No. 6,383,182, issued May 7, 2002, to Berube et al., discloses a directional ablation instrument for ablation of a targeted tissue. The instrument includes a transmission line having a proximal portion suitable for connection to an electromagnetic energy source, and an elongated antenna device having a longitudinal axis and an end coupled to the transmission line. The antenna is adapted to generate an electric field sufficiently strong to cause tissue ablation of the targeted tissue. An elongated support assembly includes a central axis, and an ablation surface extending longitudinally along an exterior surface portion of the support assembly. The support assembly is configured to receive the antenna device in the ablation surface such that the longitudinal axis of the antenna device is off-set from the support assembly central axis. Further, the antenna device is oriented toward the surface portion for positioning of the antenna device substantially adjacent to or in contact with the targeted tissue during operable use.
U.S. Pat. No. 6,527,768, issued Mar. 4, 2003, to Berube discloses a microwave ablation instrument including a transmission line having a first conductor and a second conductor suitable for the transmission of microwave energy. A horn antenna device is mounted to the end of the transmission line, and include an outer conductor and an inner conductor. The outer conductor of the horn antenna is electrically coupled to the second conductor of the transmission line, and includes a peripherally extending interior wall flaring outwardly to define a recess therein. The inner conductor of the horn antenna is electrically coupled to the first conductor of the transmission line and terminates in the outer conductor recess. The inner conductor and the outer conductor cooperate to emit an electromagnetic field sufficiently strong to cause tissue ablation in a direction generally away from the flared interior wall of the outer conductor.
U.S. Pat. No. 6,496,736, issued Dec. 17, 2002, to Carl et al., discloses an exemplary method and apparatus to treat atherosclerosis wherein the artery is partially closed by dilating the artery while preserving the vital and sensitive endothelial layer thereof. Microwave energy having a frequency from 3 GHz to 300 GHz may be propagated into the arterial wall to produce a desired temperature profile therein at tissue depths sufficient for thermally necrosing connective tissue and softening fatty and waxy plaque while limiting heating of surrounding tissues including the endothelial layer and/or other healthy tissue, organs, and blood. The heating period for raising the temperature a potentially desired amount, about 20 degrees Centigrade, within the atherosclerotic lesion may be less than about one second. In one embodiment of the invention, a radically beveled waveguide antenna is used to deliver microwave energy at frequencies from 25 GHz or 30 GHz to about 300 GHz and is focused towards a particular radial sector of the artery. Because the atherosclerotic lesions are often asymmetrically disposed, directable or focused heating preserves healthy sectors or the artery and applies energy to the asymmetrically positioned lesion faster than a non-directed bean. A computer simulation predicts isothermic temperature profiles for the given conditions and may be used in selecting power, pulse duration, beam width, and frequency of operation to maximize energy deposition and control heat rise within the atherosclerotic lesion without harming healthy tissues or the sensitive endothelium cells
U.S. Pat. No. 6,690,963, issued Feb. 10, 2004, to Ben-Haim et al., discloses a locating system for determining the location and orientation of an invasive medical instrument, for example a catheter or endoscope, relative to a reference frame, comprising: a plurality of field generators which generate known, distinguishable fields, preferably continuous AC magnetic fields, in response to drive signals; a plurality of sensors situated in the invasive medical instrument proximate the distal end thereof which generate sensor signals in response to said fields; and a signal processor which has an input for a plurality of signals corresponding to said drive signals and said sensor signals and which produces the three location coordinates and three orientation coordinates of a point on the invasive medical instrument.
U.S. Patent Application Publication No. 2002/0128642, published Sep. 12, 2002, and other publications, to Berube et al., discloses a directional ablation instrument for ablation of a targeted tissue. The instrument includes a transmission line having a proximal portion suitable for connection to an electromagnetic energy source, and an elongated antenna device having a longitudinal axis and an end coupled to the transmission line. The antenna is adapted to generate an electric field sufficiently strong to cause tissue ablation of the targeted tissue. An elongated support assembly includes a central axis, and an ablation surface extending longitudinally along an exterior surface portion of the support assembly. The support assembly is configured to receive the antenna device in the ablation surface such that the longitudinal axis of the antenna device is offset from the support assembly central axis. Further, the antenna device is oriented toward the surface portion for positioning of the antenna device substantially adjacent to or in contact with the targeted tissue during operable use.
Books with related subject matter may include the following:
“Microstrip Lines and Slotlines,” 1996, K. C. Bupta et al., published by Artech House, in Norwood Mass., in Chapter 7.
“Design of Nonplanar Microstrip Antennas and Transmission Lines,” 1999, by K. L. Wong et al, published by John Wiley & Sons, Inc., New York, N.Y., in Chapter 8.
It would be desirable to provide an antenna that can be made sufficiently small to function as a catheter or syringe antenna and to provide directionality for radiating, with azimuthal directionality, into a biological medium wherein space is not otherwise available. Those skilled in the art have long sought and will appreciate the present invention that addresses these and other problems.